Add LE connection interval sysprops

These will replace the current two sysprops below:
- min_connection_interval
- max_connection_interval
when the flag initial_conn_params_p1 is enabled.

Bug: 308483803
Bug: 378595485
Test: Manual
Change-Id: I0c7f1aa0679a9dec24ed5d6c01b92f749db59357